Tracing subterranean communication paths



COMMUNICATION June 18, 1968 J. L. OAKS TRACING SUBTERHANEANCOMMUNICATION PATHS Filed April 22, 1965 INVENTOR J. OAKS d?) 1 J it uw;

A T TORNEKS` RESERVOIR ROCK CRACKED OIL ZONE United States Patent3,388,742 TRACING SUBTERRANEAN 4CGMMUNICATION PATHS Jerald L. Oaks,Bartlesville, Okla., assignor to Phillips Petroleum Company, acorporation of Delaware Filed Apr. 22, 1965, Ser. No. 449,976 4 Claims.(Cl. 16d-4) ABSTRACT OF THE DISCLOSURE Subterranean communication pathsare established between wells communicating with a common oil-bearingstrata by injecting into one well `ste-am at a temperature and pressuresufficient to crack the crude within the strata and lform hydrogen andthereafter detecting the presence of this 'hydrogen within another wellin this .oildbearing strata.

This invention relates to a method for tracing the subterraneancommunication paths between producing wells. In one of its aspect-s, itrelates to a method for tracing subterranean passagewrays by forminghydrogen in situ at a irst wel-l and analyzing the production of asecond well for hydrogen. In another of its aspects, the inventionrelates to a method for determining the communication between aplurality of wells by injecting into a rst well la quantity of steam lata temperature and pressure suicient to crack hydrocarbons therein, andanalyzing the fluid produced at `a producing well in the vicinity ofsaid first well to detect the presence of hydrogen.

Modern oil tield practice dictates in certain circumstances thatvario-us tracts of producing wells be pooled in order to recover themaximum amount of hydrocarbons from the oi-l bearing strat-a. In theunitizing or pooling operation, it is common practice to use one of theproducing wells as an input well and other producing wells locatedaround the input well as producing wells. In one opera-tion, forexample, fluid is injected into the input well, and the fluid is used todrive the hydrocarbons toward the producing wells. In yanotheroperation, for example, combustion is initiated in the producing strata,and the pressure which builds up from such combustion will drivehydrocarbons toward the producing wel-ls.

`It is obvious from the above examples that it is a necessaryprerequisite to any secondary recovery operation in which an input andIan output well is used to know which Wells have communicating passagestherebetween. In some cases, one producing well wil-l be producinghydrocarbons from a particular strata, whereas a second producing wel-1will be producing hydrocarbons from a second producing strata. In such acase, although the producing wells cou-ld possibly be in communication,they will not be considered to be in communication for secondaryrecovery purposes.

In other instances, a lfault will disrupt communica-tion between twoproducing wells which are producing from the same strata. In mostinstances, it cannot be -determined from mere inspection of the depth ofthe well or the type of uid which is produced from the well whether ornot various wells have communicating paths therebetween.

A number of methods have been devised to determine whether la series ofproducing wells have a communicating passage therebetween. One of suchmethods contemplates injecting a boron-containing compound, `such asborax, into an input well in a water flood operation. Thereafter, theproduction from the various producing wells is tested for the presenceof boron. In such a manner the ofw of water can be -traced from inputwells to output wells. However, as is obvious lfrom the abovediscussion, this process is limited to a water tlood operation.

Another prior `art method contemplates introducing a 3,388,742 PatentedJune 18, 1968 ICC radioactive gas, such as Radon, into -a reservoirthrough `a first well and detecting the radioactivity of the strata bypositioning in other wells radioactivity detection devices. This methodrequires expensive equipment for producing and analyzing theradioactivity within the well bore. Further, radioactive material can bedangerous and must be specially handled.

Still another prior art method contempates tracing the communicatingpat-hs between well bores in 4a pressurizing operation. In such anoperation, non-condensible gases, such as CO, H2, NO, and N2, areinjected into Ian input well with repressurizing gas, normallyprincipally CH4. The non-condensible gas is then detected at theproducing well. CO, NO, and N2 can be easily detected, but theoperation, for the most part, is limited to the repressurizing type ofoperation. |Further, hydrogen is sometimes present in the repressurizinggas and the reservoir gas. Thus, if hydrogen were added to the`repressurizing gas, and detected in a producing well, it would not beclear whether the hydrogen came from the reservoir gas `or from theinput well.

I have found :a simple, inexpensive method for tracing `subterraneancommunication paths by forming hydrogen in situ and thereafter detectinghydrogen from the producing wells. I have found that this operation canbe ac-complished during a special type of secondary recovery operationin a viscous crude reservoir.

By various `aspects of this invention, one -or more of the following, orother, objects can be obtained.

It is 4an object of this invention to provide ta method for tracing theow of fluids through underground oil producing strata.

yIt is a further object of this invention to provide a simple,inexpensive method for ldetermining subterranean communication betweenvarious producing wells.

It is a still further object of this invention to provide a simplemethod for determining the subterranean communication between an inputwell and a series of output wells.

It is 'a still Vfurther :object of this invention to provide a methodfor tracing subterranean communication paths while simultaneouslycarrying out a second-ary recovery process.

Other aspects, objects, and the several advantages of this invention areapparent to one skilled in the art from a study of -t-his disclosure,the drawing, and the Iappended claims.

According to the invention, subterranean communication paths can betraced by producing hydrogen in situ in a first well, and thereafterdetecting the presence of hydrogen -in the production of `a second WellWithin the general tarea of the iirst well. Hydrogen has been found tobe a most effective tracing agent, since it has a high diffusion ratethrough porous media. The fast diffusion rate of hydrogen provides arather fast, eflicient method for tracing the subterranean communicationpaths.

In one embodiment of the invention, steam can be introduced into a iirstwell at a temperature and pressure sufficient to crack the crude aroundthe well bore in situ.

The invention contemplates injecting high pressure steam into the oilbearing formation, at a temperature in excess of 600 F., high enough toinduce in situ hydroc-racking of the crude, thereby producing hydrogenwhich, under the pressure of the steam being injected, is forced at ahigh rate through the pathways of the formation to the other wellsdrilled into the formation and communicating with the injection well.After starting the injection, the etliuent of the peripheral wells iscontinuously monitored for hydrogen production -by conventionaldetectors. After a short period of time (5-20 days), the injection wellcan be shut-in, and monitoring can =be continued for some time toprovide additional hydrogen diffusion data.

From the time needed for hydrogen evolution and the normalized`comparative quantity o f hydrogen produced from the peripheral wells, acommunication path pattern can be established. If a well fails toproduce hydrogen at the end of the test period, it may be assumed that abarrier exists to free communication and/ or that the well is producingfrom a different or `faulted horizon,

The invention c-an be further exemplified by reference to theaccompanying figure, which shows an embodiment of the invention.

Referring now to the figure, an input well 1 communicates with oilbearing strata 6 and 6. Wells 2, 3, and 4 also communicate with oilbearing strata 6 and 6 and are adapted to produce oil therefrom. Faultline 5 disrupts communication between oil bearing strata 6 and 6. Inoperation, steam is injected into well 1 and cracks the crude in zone 7of oil bearing strata 6. Because output wells 2 and 3 communicate withinput well 1, the hydrogen produced in situ in the cracked oil Zone 7will be detected in the production from wells 2 and 3. However, nohydrogen will be detected from well, 4 because communication betweenwell 1 and Well 4 are Iblocked by fault line 5.

The invention can be carried out simultaneously during a secondaryrecovery process which uses steam in an input well. In copendingapplication Ser. No. 422,833, filed Dec. 31, 1964, there is disclosedand claimed a method for the secondary recovery of a viscous crude byinjecting into a producing well steam at such a tempe-rature andpressure to cause cracking of the crude, shutting in the well for asoaking period, and then producing the well. A single well or aplurality of wells can be operated according to this invention. In suchan operation, it would :be possible to simultaneously detect hydrogenfrom the producing wells. During the steam injection period and duringthe soaking period, the production from nearby producing wells can betested for hydrogen production. Preferably, the adjacent producing wellswould not have had steam injected thereto a reasonable time prior to thetesting for hydrogen.

As is obvious from the above description, this method is especiallyapplicable to formations of highly viscous crudes in which the tracingof pathways is particularly difficult, especially by injection of uidsand chemicals. Further, therefore expensive chemical treatment andpumping can be avoided by the in situ generation of hydrogen -by thesteam cracking.

The following is a specific example of the successful operation of theinvention in the Oficina Sands of Eastern Venezuela.

Example I Steam injection into a well was terminated after days ofcontinuous steam injection. A total of 5.58 billion Btu. was injected,corresponding to about 15,200 barrels of water at reservoir conditions.At no time during this injection lperiod was there 4any evidence of abuild-up of resistance to ow. Monitoring of offset wells showed thathydrogen broke through at three of the wells, but not at a fourth offsetwell. None of these wells showed production increases. Free hydrogen wasdetected in producing wells at a distance of about 700 feet from thesteam injection well only about ten days after steam injection began. f

The above example shows that the injection of steam into an oil bearingstrata at a temperature and pressure sufficient to crack the crudetherein and the monitoring of hydrogen at near-by wells is rapid,efcient, and effective method for tracing the subterranean communicationpaths of oil bearing strata.

The following example shows how the invention can be combined with asteam injection secondary recovery operati-on.

Example II This high pressure steam cracking or hydro-cracking processwas successfully operated in the Oficina Sands of Morichal Field ofVenezuela. In-situ cracking took place:

(1) Initial production of 5.3 API oil from a reservoir in which thenative oil was approximately 14 API gravity after a 30 day 640 F. steaminjection period, followed by a 5 day soak period. The gravity graduallyincreased with time, finally exceeding the original API gravity as thelighter ends produced. Production was increased several times.

(2) The characteristic sulfurous odor of cracked oil was detected in thevicinity of the -oil after steam injection indicating that the processoperated successfully.

(3) Free hydrogen was detected in the produced stream of oil producedfrom nearby wells communicating with the injection Well.

The advantages of high temperature steam cracking of oil in place are:no combustion, no destruction of oil by burning, increased recovery ofoil in place, less danger of well fires, yand improved recovery ofhighly viscous crudes.

The above example shows that the free hydrogen, detected in the producedstream of oil produced from nearby Wells, indicates the communication ofthe injection well with the producing well simultaneously while carryingout the secondary recovery operation.

It is obvious thatin carrying out the invention, where the producingstrat-a sought to :be tested is low in hydrogen producing materials, theinjection fluid can also contain small amounts of hydrogen to supplementhydrogen formed therein.

Reasonable variation and modification are possible within the scope ofthe foregoing disclosure, ,the drawing and the appended claims to theinvention, the essence of which is that subterranean communication pathscan be traced by forming hydrogen in situ in a first well and testingthe production of a second well for hydrogen.

I claim:

1. A method for tracing subterranean communication paths between aninput well and an output well in communication with oil-bearing stratacontaining high viscosity crude, in which the strata communicationbetween existing wells has not been established, said method comprisinginjecting into said input well steam at a temperature and pressuresufficient to crack the crude therein, thereby forming hydrogen in thecracking process, and thereafter detecting hydrogen from said outputwell in the vicinity of said input well.

2. A method according to claim 1 wherein the temperature of said steamis at least 600 F.

3. A method for detecting a flow path between a first well and a secondwell communicating with oil-bearing strata containing viscous crudewhile simultaneously recovering hydrogen from said strata in whichcommunication between existing well walls has not been established, saidmethod comprising injecting into said first well steam at a temperatureand pressure sufficient to crack the crude in said strata, shutting saidfirst well in for a soaking period, and producing said first well, andsimultaneously during said steam injection, said shutting in period, andsaid producing period, detecting hydrogen at said second well, saidsecond well not having had steam injected therein a reasonable timeprior to the detecting period.

4. A method according to claim 3 wherein said second well is a producingweil.

References Cited UNITED STATES PATENTS 2,318,689 5/1943 Hodell et al166-4 X 2,800,183 7/1957 Jenkins 166-4 2,843,207 7/1958 Clenell 166-42,958,519 11/1960 Hurley 166-11 X 3,044,543 7/1962 Ramey 166-4 3,259,1867/1966 Dietz 166-11 3,284,281 11/1966 Thomas 166--11 STEPHEN J. NOVOSAD,Primary Examiner.

